User Guide

14 Copyright © Acronis, Inc., 2000-2007
Chapter 3. General information and
proprietary Acronis technologies
3.1 The difference between file archives and disk/partition images
A backup archive is a file or a group of files (also called in this Guide “backups”), that
contains a copy of selected files/folders data or a copy of all information stored on selected
disks/partitions.
When you back up files and folders, only the data, along with the folder tree, is compressed
and stored.
Backing up disks and partitions is performed in a different way: Acronis True Image Server
stores a sector-by-sector snapshot of the disk, which includes the operating system, registry,
drivers, software applications and data files, as well as system areas hidden from the user.
This procedure is called “creating a disk image,” and the resulting backup archive is often
called a disk/partition image.
Acronis True Image Server stores only those hard disk parts that contain data (for supported
file systems). Further, it does not back up swap file information (pagefile.sys) and
hiberfil.sys (a file that keeps RAM contents when the computer goes into hibernation). This
reduces image size and speeds up image creation and restoration.
A partition image includes all files and folders independent of their attributes (including
hidden and system files), boot record, FAT (file allocation table), root and the zero track of
the hard disk with master boot record (MBR).
A disk image includes images of all disk partitions as well as the zero track with master boot
record (MBR).
By default, files in all Acronis True Image Server archives have a “.tib” extension.
It is important to note that you can restore files and folders not only from file archives, but
from disk/partition images, too. To do so, mount the image as a virtual disk (see
Chapter 11.
Mounting an image as a virtual drive
) or start the image restoration and select Restore
specified files or folders.
3.2 Full, incremental and differential backups
Acronis True Image Server can create full, incremental and differential backups.
A full backup contains all data at the moment of backup creation. It forms a base for
further incremental or differential backup or is used as a standalone archive. A full backup
has the shortest restore time as compared to incremental or differential ones.
An incremental backup file only contains data changed since the last full or incremental
backup creation. Therefore, it is smaller and takes less time to create. But as it doesn’t
contain all data, all the previous incremental backups and the initial full backup are required
for restoration.
Unlike incremental backup, when every backup procedure creates the next file in a “chain,” a
differential backup creates an independent file, containing all changes against the initial
full archive. Generally, a differential backup will be restored faster than an incremental one,
as it does not have to process through a long chain of previous backups.